In that case, I assume that treasure eliminated via an Isle of Fire would have to be revealed in a 1v1 standard game?
I would think it still doesn’t get revealed, because since abilities that add to the original 30 gold don’t change the requirements of the more than half rule (16 gold), it seems like subtractions from the total amount of starting gold would also not affect the required total of 16+. Eliminating treasure just makes that endgame condition less likely (or impossible if a lot of coins are eliminated), so the game is more likely to end with all treasure unloaded to HI’s or no future move actions.
There’s no specific trigger to reveal treasure when it’s removed or eliminated by some method other than sinking a ship (in order to split it).
In a casual 1 vs 1 game it’s probably still a good idea to reveal it, just so both players will be aware if the “more than half” condition has become impossible for anyone to reach, forcing them to rely on one of the other endgame conditions instead.
Adding to or subtracting from the actual total amount of gold in play never changes the target value. That remains fixed in place based on what the game started with.